1. Field of the Invention
This invention relates to a magnetic head assembly of a disk drive of the double-sided recordable type wherein information can be read from and written on either side of a disc-shaped magnetic recording medium.
2. Description of the Prior Art
In disk drives of the double-sided recordable type wherein the readout and write operation of a disc-shaped magnetic recording medium (hereinafter referred to simply as a disk) can be performed on either side, there are known three systems classified depending upon the mounting of gimbal spring of at least one of two magnetic heads: the lower-fixed upper-movable system wherein the gimbal spring is disposed on the side of an upper hold case, the upper-fixed lower-movable system wherein the gimbal spring is disposed on the side of a lower carriage, and the upper-movable lower-movable system wherein the gimbal springs are disposed on both the carriage and hold case. Among these systems, the lower-fixed upper-movable system is widely adopted because the carriage disposed on the lower side is guided directly by a guide rod so that a reference plane of the disk can easily be defined. Contrarily, the upper-fixed lower-movable system has the problem that the reference plane is difficult to define when the hold case is supported pivotably on the carriage. Additionally, though having good tracking performance, the upper-movable lower-movable system is rarely adopted actually because the reference plane is as difficult to define as in the upper-fixed lower-movable system.
Compared with the first-mentioned lower-fixed upper-movable system, the second-mentioned upper-fixed lower-movable system has difficulty fixing the reference plane, but seems to have better tracking performance; thus, its progress is expected. That is, because the hold case on the upper side has two movable portions in the gimbal spring and in the coupling portion of the hold case with the carriage, the lower-fixed upper-movable system causes a secondary lag in the tracking operation of the two movable portions if there is a deformation of the disk; thus its tracking performance is degraded. On the contrary, in the upper-fixed lower-movable system, the position of the magnetic head on the upper side fluctuates little and the movable portion of the magnetic head on the lower side exists only in the gimbal spring; thus, there appears no lag in the secondary tracking operation of this system seems to be advantageous in terms of the tracking performance. Under the foregoing circumstances one invention has been proposed in Japanese Patent Application Laid-Open No. 57-147160. This prior system is illustrated in FIG. 2.
The magnetic head support mechanism shown in FIG. 2 is composed principally of an arm (hold case) 34 on which a magnetic head 32 is mounted and a carriage 36 on which a magnetic head 33 is mounted. The arm 34 is attached turnably by means of a plate spring-like hinge 35 projecting from a side portion 36a of the carriage 36, and a given load pressure is created by means of a coil spring 37 coupled to an upper portion 36b of the carriage 36. The upper magnetic head 32 is fixed directly on the under surface of the arm 34, and the lower magnetic head 33 is attached via a gimbal plate 38 to the upper surface of the carriage 36, so that the upper magnetic head 32 and lower magnetic head 33 are opposed mutually with a disk (flexible disk) 31 put therebetween. In a thru-hole formed in a lower portion 36c of the carriage 36 at a position corresponding to the under surface of the gimbal plate 38, there is provided a support plate spring 41 having a pivot 40 at its point, which pushes the gimbal plate 38 toward the disk 31 form below.
In the magnetic head support mechanisms as above of the prior system, accuracy cannot be ensured with respect to the reference plane of the magnetic head 32 because positioning of the arm 34 is achieved only by means of the plate spring-like hinge 35. Thus, even when the tracking performance of the magnetic heads 32 and 33 is enhanced, the overall read/write characteristic cannot be improved if the degree of accuracy of the reference plane falls.
With such conventional magnetic head support construction, since the pivot 40 supporting the gimbal plate 38 is supported by the leaf spring 41, the lower magnetic head 33 is sunk or lowered after the upper and lower magnetic heads 32, 33 have been brought into engagement with each other via the disk 31, and in this lowered position the resilient force of the leaf spring 41 and the pressing force of the coil spring 37 are balanced or become stable. In this stable position, the upper and lower magnetic heads 32, 33 are parallel to the reference plane of the disk 31, whereupon recording and play back can take place.
However, when the stable position of the magnetic heads relative to the disk is assumed by lowering of the lower magnetic head 33, the corner 32a of the upper magnetic head 32 adjacent to the hinge 35, preceding the other portions of the upper magnetic head 32, is brought into contact with the disk 31. At that time, since the arm 34 is pressed by the coil spring 37, all of the load pressure of the coil spring 37 is exerted concentratedly on this corner 32a, thus impairing the disk 31.